A competent way to do this would be to detect if the user has typed something into a field on the page and pop up a notification, then go back if they push twice, instead of removing standard functionality of the browser and then attempting to hack it back in with an extension.

[SOLVED]
I think the extension is working, however not for websites that auto focus on the search box when the page loads. Could be because the extensions then thinks you are filling out a form and prevents the backspace behaviour. So I suppose this bug is resolved as the issue is with the website itself, rather than the extension.

For example, http://www.ebay.co.uk/

Ah, yes -- once focus is in an editable box, backspace acts as an editing key rather than navigating. I expect that's how it behaved previously as well, but I'll have to dig up an old version to check.

Thanks for the followup!